Images sometimes need to be analyzed to determine whether they are blank or nearly blank. An image is blank when it appears to a user to be a single, solid color. An image is nearly blank when a dominating portion of it appears to a user to be a single, solid color. An example of a nearly blank image is a black screen with a corporate or television network logo appearing in a portion (e.g., corner) of the screen. Such a nearly blank screen may be displayed by a television network between a program and an advertisement. Because nearly blank images can be considered to be blank from a viewer's perspective, the term “blank” in this specification includes actually blank and nearly blank.
An image that is selected from a video may need to be analyzed to determine whether it is blank. A video is generally a sequence of images (e.g., “frames”), or a sequential set of key frames and delta frames. A key frame describes an image completely and delta frames describe portions of the key frame's image that change before a subsequent key frame is received from the sequence. An image can be selected from the video to identify the video. As an example, an Internet World Wide Web (“Web”) page may display a “thumbnail” image to identify a linked video. When a user viewing the Web page selects the thumbnail image, the linked video may play.
The image may be selected automatically. As an example, when a Web site enables users to upload videos, the Web site may automatically select a thumbnail image to associate with the video to provide a link to the video. Commonly, the image is selected from a frame near the beginning of the video, end of the video, or randomly. Sometimes, the automatically selected image is blank. This can occur because some videos have transitions from a solid color (commonly white or black), such as near the beginning of the video.
When the selected image is blank, the image is not a useful thumbnail image because a user viewing a Web page containing the blank image would not readily know to which video the image relates. It is thus desirable to select images that are not blank.